Health Assessment Dietary Exposure and Maximum Residue Limits (MRLs)

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Monique Thomas
A/Section Head
Exposure Assessment Section I
Health Evaluation Directorate

Food Residue Chemistry Studies

• Residue Chemistry Guidelines (DIR98-02) outline the residue chemistry data requirements
• These requirements for the registration of new products/new uses are the same as the requirements for products under re-evaluation
• The Canadian residue chemistry requirements are consistent with the U.S. EPA residue chemistry requirements (OPPTS 860.1000)

Food Residue Chemistry Studies

• Label
• Plant and livestock metabolism studies
• Confined accumulation in rotational crops
• Analytical methods -plant and animal matrices
• Storage Stability -plant and animal matrices
• Crop Field Trials -Primary crops (MRLs, DRA)
• Field Accumulation in rotational crops -Secondary crops (MRLs, DRA)
• Processing studies (MRLs, DRA)
• Livestock feeding studies (MRLs, DRA)

DACO 1.0 -Label

• Identifies petitioned uses (i.e. crops/crop groups)
• Identifies use directions
  • Rate of application
  • Number of applications/season
  • Re-treatment interval
  • Pre-harvest interval (PHI)
  • Plant-back intervals
  • Type of application (ground or aerial)

DACO 6.2 - Livestock Metabolism Studies

• Elucidate the nature of the residue in animal matrices (e.g. meat, milk and eggs)
• Identify the metabolites and degradates that may occur after livestock animals (ruminants and/or poultry) are exposed, either directly or indirectly, to a pesticide
  • Which metabolites must be included in dietary risk assessment?
  • Which metabolites must be included in MRL/tolerance expression?

DACO 6.3 - Plant Metabolism Studies

• Elucidate the nature of the residue in plant commodities (e.g. cereal grain, root vegetable, leafy vegetable)
• Identify the metabolites and degradates that may occur in a food as a result of pesticide use.
  • Which metabolites must be included in dietary risk assessment?
  • Which metabolites must be included in MRL/tolerance expression?

DACO 7.2 - Residue Analytical Methods

• Quantify the pesticide and the associated metabolites/degradates that must be included in the tolerance expression for plant and animal commodities, as identified in the metabolism studies.
• Qualify as an enforcement method if it:
  • is specific to the analytes of interest;
  • Is validated by an independent laboratory; and
  • demonstrates acceptable extraction efficiency.

DACO 7.3 - Freezer Storage Stability Studies

• Determine whether the residues of the pesticide and the metabolites/degradates are stable in stored plant and animal commodities.
• Measure the degree of loss or degradation during storage.
• Insure the integrity of the residues reported in many of the food residue chemistry studies (e.g. metabolism, crop field trials, field crop rotation).
• If acceptable freezer storage stability data is provided for five diverse crops, additional storage stability studies may be waived.

DACO 7.4.1 - Supervised Crop Field Trials

• Determine the magnitude of the residue in or on raw agricultural commodities (RACs) after treatment with the pesticide according to approved label directions.
• Conducted in representative growing regions to account for different soil types, pest pressure and climate.
• Number of trials may vary from 3 to 20.
• The residue levels form the basis for the establishment of the MRLs.

DACO 7.4.2 - Residue Decline Studies

• Determine the rate of decline of residues between application and harvest.
• Determine if residues are higher at longer preharvest intervals (PHIs) than requested.
• Determine the approximate half-life of the pesticide.

DACO 7.4.3 - Confined Accumulation in Rotational Crops - DACO 7.4.4 - Field Accumulation in Rotational Crops

• A rotational crop is a crop that is planted in a field following harvest of the primary crop.
• Rotational crops may contain residues resulting from pesticide applications to the primary crop.
• Confined (radiolabel) and field (cold) rotational crop studies determine the nature and magnitude of pesticide residue uptake into rotational crops.

DACO 7.4.5 - Food Procssing Studies

• Estimate a processing factor that describes the concentration or reduction of pesticide residues going from the raw to processed commodity (e.g. apples to juice).
• Required for all processed foods.

DACO 7.5 - Livestock Feeding Studies

• Quantify the magnitude of the residues in meat, milk and eggs resulting from livestock consumption of treated feed, or direct application to livestock.
• The residue levels form the basis for the establishment of the MRLs for animal matrices.

Secondary Residues

Secondary Residues Components of Dietary Risk Assessment

• Residue - Level of the pesticide in foods.
• Consumption - Amount and types of foods consumed in a given period of time.
• Toxicology endpoints - Acceptable Daily Intake (ADI), Acute Reference Dose (ARfD), Cancer Risk.

Residue Inputs

• Maximum Residue Limit (MRL)
• Median residue values
• Storage degradation
• Processing studies (concentration factors)
• Cooking studies (when available)
• Theoretical residues in livestock tissues
• Blended commodities
• % crop treated -market share
• Monitoring data (CFIA)
• Market Basket Surveys-purchased foods

Consumption Information

• Dietary Exposure Evaluation Model - Food Commodity Intake Database (DEEM-FCID, Version 2.03).
• USDA Continuing Survey of Food Intakes by Individuals (CSFII): 1994-1996, 1998 (children specific) - 2 days.
• All geographical areas, all ethnic groups, all age groups, both sexes; monitoring across all seasons; large number of respondents.

Exposure Scenarios

• Chronic exposure = average amount of pesticide residue a person might consume every day over extended periods (several months to lifetime).
• Acute exposure = amount that might be ingested on a single day.

Dietary Risk Assessment

Potential Daily Intake (PDI) = Residue * Consumption

Dietary Risk = Potential Daily Intake ÷ ADI or ARfD or Cancer Risk

Potential Daily Intake (PDI)

• Estimated for various subpopulations and age groups, including infants, toddlers, children, adolescents and adults.
• Accounts for residues in food from both domestic and imported sources.
• Acceptable Risk
  • If PDI does not exceed the ADI, ARfD, or cancer risk, risk is acceptable, MRLs may be established.

Why Establish Maximum Residue Limits?

• Domestically, as an enforcement tool to ensure compliance with the Canadian registered pesticide label.
• To ensure that food commodities that move in trade
  (i.e. imported) comply to an acceptable residue level that is protective of human health.

Current MRL-Setting Process

• The current process for setting MRLs requires amending the Food and Drug Regulations (FDR) via the Gazetting process - routine, but cumbersome.

New MRL-Setting Process

• Once in force, Bill C-28, which received Royal Assent in November 2005, will:
  • legally recognize the pesticide MRLs specified under the PCPA; and
  • deem all existing MRLs (Table II, Division 15 of the FDR) to have been established under the PCPA so there are no legislative gaps.
• MRLs will continue to be scientifically determined;
• Domestic and international (i.e. World Trade Organization) consultations will still take place when MRLs are established, amended or revoked; and
• MRLs will continue to be enforceable by CFIA.

Reference List

• Residue Chemistry Guidelines, DIR98-02
• General Principles for Performing Aggregate Exposure and Risk Assessments, SPN2003-04
• Assessing Exposure from Pesticides in Food - A User's Guide, SPN2003-03